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Configuring the DHCP relay agent
Overview
The DHCP relay agent enables clients to get IP addresses from a DHCP server on another subnet.
This feature avoids deploying a DHCP server for each subnet to centralize management and reduce
investment. Figure 30 sh
ows a typical application of the DHCP relay agent.
Figure 30 DHCP relay agent application
An MCE device acting as the DHCP relay agent can forward DHCP packets between a DHCP server
and clients on either a public network or a private network. For more information about MCE, see
MPLS Configuration Guide.
Operation
The DHCP server and client interact with each other in the same way regardless of whether the relay
agent exists. For the interaction details, see "IP address allocation process." The follo
wing only
describes steps related to the DHCP relay agent:
1. After receiving a DHCP-DISCOVER or DHCP-REQUEST broadcast message from a DHCP
client, the DHCP relay agent processes the message as follows:
a. Fills the giaddr field of the message with its IP address.
b. Unicasts the message to the designated DHCP server.
2. Based on the giaddr field, the DHCP server returns an IP address and other configuration
parameters in a response.
3. The relay agent conveys the response to the client.
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